1. Technical Field
The present invention relates generally to a baghouse, a filter assembly for use in the baghouse and a method of installing the filter assembly in the baghouse. In particular, the present invention relates to a relatively long multi-piece filter assembly having pleated filter elements.
2. Description of the Prior Art
Continuous emphasis on environmental quality results in ever-increasing regulatory control on pollutants and emissions throughout the world. Much of the regulatory control is focused on reducing pollutants and emissions from certain industrial plants, such as power plants and metal production plants. A known technique to control pollutants and emissions from industrial plants is to separate undesirable particulate matter carried in a gas stream by fabric filtration. Such fabric filtration is accomplished in a dust collection apparatus known in the industry as a "baghouse."
The baghouse typically includes a housing divided into two plenums by a tubesheet. One plenum is a "dirty air plenum" which communicates with an inlet and receives "dirty" or particulate laden gas from a source at the plant. The other plenum is a "clean air plenum" which receives cleaned gas after filtration and communicates with an outlet to direct cleaned gas away from the baghouse. A plurality of relatively long cylindrical fabric filters, commonly called "bags," are suspended from the tubesheet in the dirty air plenum. Each bag is installed over a cage and has a closed lower end. The cage may be in two or more pieces. Each bag is mounted to the tubesheet at its upper end to hang vertically in the dirty air plenum. The upper end portion of the bag is open and the interior of each bag is in fluid communication with the clean air plenum.
In operation, particulate laden gas is conducted into the dirty air plenum. As the particulate laden gas flows through the baghouse, the particulates carried by the gas engage the exterior of the fabric filter bags and accumulate on the fabric filter bags or are separated from the gas stream and fall into an accumulator chamber at the lower portion of the dirty air plenum. Cleaned gas then flows through the fabric filter bags, into the interior of the fabric filter bags, into the clean air plenum and through the outlet. Although many baghouses are made according to this basic structure, there may be numerous operational and structural differences among baghouses.
There is interest in replacing known fabric filter bags with pleated element filters to increase the effective filtering area while occupying the same space, or less, within the baghouse as the known fabric filter bags. However, certain barriers to easy replacement of fabric filter bags by pleated element filters exist. In some baghouse designs, the fabric filter bags can have a length of about four meters. The clean air plenum often has a clearance height that is substantially less than four meters, for example, about one and a half meters. It is generally not a problem to install fabric filter bags in the baghouse since the fabric filter bags are foldable, flexible and non-rigid. A relatively long and rigid pleated element filter cannot be installed without considerable manipulations if it can be installed at all, even if the baghouse has a roof with a portion that can be moved to a position which provides access to the clean air plenum. Not all baghouses have such a movable roof.
In order to occupy the same space within the baghouse as a fabric filter bag, the length of the pleated element filter would be relatively long and can be up to about four meters in length or more. This presents a problem for filter manufacturers because there are limits as to the width of the filter media that can be pleated with current production machinery to provide such a long filter. The current production machinery used to pleat filter media typically cannot accommodate continuous filter media more than about two meters in width. Such a long filter would also be relatively difficult to handle and transport.
If the more efficient pleated element filter is desired, the majority of the filter must be capable of being inserted through an opening in the tubesheet from the clean air plenum. If known, relatively short, pleated element filter structures are used and are axially connected together, more problems can arise. Any structure used to connect known pleated element filter structures together must be strong enough to carry the load of the filter when it has particulates accumulated on it and fit through an opening in the tubesheet. Furthermore, a potting material, such as silicone or polyurethane, is typically used to hold a pleated element in a known filter structure and connect other structure of the filter together. This potting material has limited ability to carry load. The weight of filters supported by the potting material is relatively large and can exceed the potting material's ability to carry sufficient load. For example, if a "clean" filter having a pleated element and a length of about four meters weighs twenty pounds, it is estimated that particulates which accumulate on the pleated element could add 200 to 300 pounds to the weight of the filter structure.
It is, thus, seen that using pleated element filters in baghouses is very desirable. Accordingly, there is a need in the industry for improvements in filter structure and installation techniques.